Recreational pools such as swimming pools and spas and many other liquid handling systems use centrigual pumps to move the liquid e.g. through conditioning devices such as filters and heaters. Centrifugal pumps efficiently move liquid by drawing the liquid in at the center of an impeller and expelling it outward, centrifugally, under considerable pressure. The flow direction of the liquid is determined by a housing which encloses the impeller and defines inlet and outlet. The impeller is driven by a motor beyond the pump housing. A shaft from the motor passes through the housing wall to the impeller. A seal is provided between the shaft and the housing wall, typically of a resilient material which through frictional engagement seals the shaft in liquid-tight relation. This seal is subject to premature failure because of heat. Heat from frictional contact at the seal and by conduction along the shaft from the motor may distort the seal material or its support, cause cracking or other seal deterioration, shortened seal life and premature failure.
Previous efforts to lengthen centrifugal seal life have included porting the impeller so that liquid flows to the seal area as a heat sink. This expedient is disadvantageous in that the efficiency of the pump is reduced by such porting, and the ability to self-prime adversely affected. Others have used a good heat conductor as a heat sink in the seal area, such as a copper cup between the housing wall and the seal material. This approach has the disadvantage of introducing a corrodible material into the system, a considerable problem in hostile environments such as swimming pool water.